PUBLISH 

UNITED STATES COURT OF APPEALS 

FOR THE TENTH CIRCUIT 

_____________________________________ 

W. CLARK APOSHIAN, 

 Plaintiff - Appellant, 

v. 

WILLIAM BARR, Attorney General of the 

United States; UNITED STATES 

DEPARTMENT OF JUSTICE; THOMAS 

E. BRANDON, Acting Director Bureau of 

Alcohol Tobacco Firearms and Explosives; 

BUREAU OF ALCOHOL TOBACCO 

FIREARMS AND EXPLOSIVES, 

 Defendants - Appellees. 

------------------------------ 

CATO INSTITUTE AND FIREARMS 

POLICY COALITION; DUE PROCESS 

INSTITUTE, 

 Amicus Curiae. 

No. 19-4036 

_________________________________ 

Appeal from the United States District Court 

for the District of Utah 

(D.C. No. 2:19-CV-00037-JNP-BCW)

_________________________________ 

Caleb Kruckenberg, Litigation Counsel (Steve Simpson and Harriet Hageman, Senior 

Litigation Counsel; and Mark Chenoweth, General Counsel, with him on the briefs), New 

Civil Liberties Alliance, Washington, DC, appearing for Appellant. 

Brad Hinshelwood, Attorney, Civil Division, United States Department of Justice, 

Washington, DC (Joseph H. Hunt, Assistant Attorney General, Civil Division, United 

FILED 

United States Court of Appeals 

Tenth Circuit 

May 7, 2020

Christopher M. Wolpert 

Clerk of Court
2 

States Department of Justice, Washington, DC; John W. Huber, United States Attorney, 

Office of the United States Attorney for the District of Utah, Salt Lake City, Utah; Mark 

B. Stern, Michael S. Raab, and Abby C. Wright, Attorneys, Civil Division, United States 

Department of Justice, Washington, DC, with him on the briefs), appearing for 

Appellees. 

Ilya Shapiro, Washington, DC, for Amicus Curiae Cato Institute. 

John D. Cline, San Francisco, California, for Amicus Curiae Due Process Institute. 

_________________________________ 

Before BRISCOE, MORITZ, and CARSON, Circuit Judges. 

_________________________________ 

BRISCOE, Circuit Judge. 

_________________________________ 

 Plaintiff-Appellant W. Clark Aposhian has filed an interlocutory appeal from the 

district court’s denial of his motion for a preliminary injunction. The district court 

concluded that Mr. Aposhian had not shown a likelihood of success on the merits of his 

challenge to a rule promulgated by the Bureau of Alcohol, Tobacco, Firearms, and 

Explosives (ATF) that classifies bump stocks as machine guns under the National 

Firearms Act (NFA), 26 U.S.C. §§ 5801–5872. See Bump-Stock-Type Devices, 83 Fed. 

Reg. 66,514 (Dec. 26, 2018) (Final Rule). The Final Rule was promulgated to clarify the 

definition of “machinegun” as found in 26 U.S.C. § 5845(b).1

 It is that definition of 

machine gun and the Final Rule that are the focus of this appeal. Exercising jurisdiction 

pursuant to 28 U.S.C. § 1292(a)(1), we agree with the outcome reached by the district 

court that Mr. Aposhian has failed to establish a likelihood of success on the merits of his 

challenge to the Final Rule, and we affirm the denial of preliminary injunctive relief. 

1

 We use the two-word spelling of machine gun except when quoting sources.
3 

I 

Statutory Framework 

The NFA (i) regulates the production, dealing in, possession, transfer, import, and 

export of covered firearms; (ii) creates a national firearms registry; and (iii) imposes 

taxes on firearms importers, manufacturers, and dealers, as well as specified transfers of 

covered firearms. 26 U.S.C. §§ 5801–5861. Failure to comply with the NFA’s 

requirements results in penalties and forfeiture and subjects the violator to the general 

enforcement measures available under the internal revenue laws. Id. §§ 5871–5872. 

“Machinegun[s]” are subject to regulation and registration under the NFA. Id. 

§ 5845(a). The NFA defines a “machinegun” as “any weapon which shoots, is designed 

to shoot, or can be readily restored to shoot, automatically more than one shot, without 

manual reloading, by a single function of the trigger.” Id. § 5845(b). The definition also 

includes “the frame or receiver of any such weapon,” as well as “any part” or 

“combination of parts designed and intended, for use in converting a weapon into a 

machinegun,” and “any combination of parts from which a machinegun can be 

assembled” as long as those “parts are in the possession or under the control of a person.” 

Id. 

Congress expressly charged the Attorney General with the “administration and 

enforcement” of the NFA, id. § 7801(a)(1), (a)(2)(A), and provided that the Attorney 

General “shall prescribe all needful rules and regulations for the enforcement of” the 

NFA, id. § 7805; see id. § 7801(a)(2)(A). 
4 

The Gun Control Act of 1968 (GCA), 18 U.S.C. § 921 et seq., as amended by the 

Firearm Owners’ Protection Act, Pub. L. No. 99-308, 100 Stat. 449 (1986), imposes both 

criminal prohibitions and a regulatory licensing scheme on certain firearm transactions. 

See 18 U.S.C. § 922 (criminal prohibitions); id. § 923 (licensing scheme). The GCA 

incorporates by reference the definition of machine gun in the NFA. See id. § 921(a)(23). 

The GCA also expressly delegates administrative and rulemaking authority to the 

Attorney General to “prescribe only such rules and regulations as are necessary to carry 

out the provisions of this chapter.” Id. § 926(a). The Attorney General has delegated the 

responsibility for enforcing and administering the NFA and the GCA to ATF. See 28 

C.F.R. § 0.130(a). 

Under 18 U.S.C. § 922(o), it is “unlawful for any person to transfer or possess a 

machinegun.” Conversely, many firearms requiring a distinct pull of the trigger to shoot 

each bullet are lawful. See generally id. § 922; 26 U.S.C. § 5845. Over time, ATF has 

promulgated regulations and issued rulings defining various terms in the NFA and GCA 

and classifying weapons and parts as machine guns. 

Regulation of Bump Stocks 

A “bump stock” is a device that replaces the standard stationary stock of a 

semiautomatic rifle—the part of the rifle that generally rests against the shooter’s 

shoulder—with a sliding, non-stationary stock that permits the shooter to rapidly increase 

the rate of fire, approximating that of an automatic weapon. Final Rule at 66,516. A 

bump stock does so by channeling the recoil energy from each shot “into the space 

created by the sliding stock (approximately 1.5 inches) in constrained linear rearward and 
5 

forward paths.” Id. at 66,518. The bump stock “harnesses the firearm’s recoil energy as 

part of a continuous back-and-forth cycle that allows the shooter to attain continuous 

firing” following a single pull of the trigger, producing a rapid bumping of the trigger 

against the shooter’s stationary finger. Id. at 66,533. That design allows the shooter, by 

maintaining constant rearward pressure on the device’s extension ledge2

 with the trigger 

finger as well as forward pressure on the front of the gun, to fire bullets continuously and 

at a high rate of fire to “mimic automatic fire.” Id. at 66,516. This continuous cycle of 

fire-recoil-bump-fire lasts until the shooter releases the trigger by removing his finger 

from the extension ledge, the weapon malfunctions, or the ammunition is exhausted. Id.

at 66,519. 

 The Attorney General, exercising his regulatory authority, first included a bump 

stock device—the Akins Accelerator—within the statutory definition of “machinegun” in 

2006. See ATF Ruling 2006-2; see also Akins v. United States, 312 F. App’x 197, 199 

(11th Cir. 2009). The Akins Accelerator, unlike many bump stocks, used “an internal 

spring” to “reposition and refire” the firearm. Akins, 312 F. App’x at 198. ATF later 

limited the devices it defined as machine guns by concluding that bump stocks that 

operated without an internal spring were not machine guns. Final Rule at 66,514. 

On October 1, 2017, a shooter in Las Vegas, Nevada, used multiple semiautomatic 

rifles equipped with bump stocks to fire several hundred rounds of ammunition into a 

2

 The extension ledge or “finger rest” is where the “shooter places the trigger 

finger while shooting the firearm.” Final Rule at 66,516. 
6 

crowd of concert attendees within a short period of time. Id. at 66,516.3

 The “‘rapid fire’ 

operation” of the shooter’s weapons enabled by the bump stocks left 58 dead and 

approximately 500 wounded. Id. In response, President Trump directed the Department 

of Justice “to propose for notice and comment a rule banning all devices that turn legal 

weapons into machineguns.” Application of the Definition of Machinegun to “Bump 

Fire” Stocks and Other Similar Devices, 83 Fed. Reg. 7,949, 7,949 (Feb. 20, 2018). ATF 

then revisited the status of bump stocks, reviewed its earlier determinations for bumpstock-type devices issued between 2008 and 2017, and decided to clarify by the 

rulemaking process the statutory terms “automatically” and “single function of the 

trigger” as applied in defining what is or is not a machine gun. Final Rule at 66,514–

66,515. On March 29, 2018, then-Attorney General Sessions issued a Notice of Proposed 

Rulemaking that suggested “amend[ing] the [ATF] regulations to clarify that [bump 

stocks] are ‘machineguns’” under 26 U.S.C. § 5845(b). See Bump-Stock-Type Devices, 

83 Fed. Reg. 13,442 (March 29, 2018). 

ATF promulgated its Final Rule on December 26, 2018. Regarding the statutory 

definition of machine gun, the Final Rule provided that the NFA’s use of “the term 

‘automatically’ as it modifies ‘shoots, is designed to shoot, or can be readily restored to 

shoot,’” 26 U.S.C. § 5845(b), “means functioning as the result of a self-acting or self3

 Because ATF had not regulated certain types of bump stocks under the NFA or 

GCA, they were not marked with a serial number or other identification markings. As a 

result, individuals were able to legally purchase bump stocks without undergoing 

background checks or complying with any other federal regulations applicable to 

firearms. Final Rule at 66,516. 
7 

regulating mechanism that allows the firing of multiple rounds through a single function 

of the trigger.” Final Rule at 66,553–66,554 (codified at 27 C.F.R. §§ 447.11, 478.11, 

479.11). The Final Rule further defined “single function of the trigger,” 26 U.S.C. 

§ 5845(b), to mean “a single pull of the trigger and analogous motions.” Final Rule at 

66,553–66,554 (codified at 27 C.F.R. §§ 447.11, 478.11, 479.11). 

Given those definitions, the Final Rule concluded that the statutory term 

“‘machinegun’ includes a bump-stock-type device”—that is, “a device that allows a 

semiautomatic firearm to shoot more than one shot with a single pull of the trigger by 

harnessing the recoil energy of the semiautomatic firearm to which it is affixed so that the 

trigger resets and continues firing without additional physical manipulation of the trigger 

by the shooter.” Id. (codified at 27 C.F.R. §§ 447.11, 478.11, 479.11). 

For its authority to promulgate the Final Rule, ATF relied on both the “plain 

meaning” of the NFA and the Attorney General’s delegation to the agency to administer 

and enforce the NFA and GCA. Id. at 66,527. In addition, ATF stated that if 26 U.S.C. 

§ 5845(b) is ambiguous, the Final Rule “rests on a reasonable construction.” Id. (citing 

and invoking Chevron U.S.A., Inc. v. Nat. Res. Def. Counsel, 476 U.S. 837 (1984)). ATF 

explained that although Congress defined “machinegun” in the NFA, “it did not further 

define the components of that definition . . . Congress thus implicitly left it to the 

[Attorney General] to define ‘automatically’ and ‘single function of the trigger’ in the 

event those terms are ambiguous.” Id.

ATF stated that the Final Rule would become “effective” on March 26, 2019, 

ninety days after promulgation. Id. at 66,514. ATF stated further that individuals would 
8 

be subject to “criminal liability only for possessing bump-stock-type devices after the 

effective date of regulation, not for possession before that date.” Id. at 66,525. Bumpstock owners were directed to destroy their devices or leave them at an ATF office by 

March 26, 2019. Id. at 66,514. 

Procedural History 

 Mr. Aposhian purchased a Slide Fire bump stock before the Final Rule was 

promulgated. He filed suit against various governmental officers and agencies 

challenging the Final Rule as unconstitutional and in violation of the Administrative 

Procedure Act (APA), arguing that the Final Rule contradicts an unambiguous statute, 26 

U.S.C. § 5845(b), and mistakenly extends its statutory definition of “machinegun” to 

cover bump stocks. The government also argued the statute is unambiguous but that the 

Final Rule is merely interpretive and, as so, reflects the best interpretation of the statutory 

text. For its part, the district court did not specifically opine on whether the statute was 

ambiguous or not. 

Ultimately, the district court denied Mr. Aposhian’s motion for a preliminary 

injunction, concluding that because the Final Rule represented the best reading of the 

statute, Mr. Aposhian was not likely to succeed on the merits of his challenge. Aplt. 

App. at 181. Because it concluded that Mr. Aposhian was unlikely to succeed on the 

merits, the district court did not reach the other three preliminary-injunction factors. See 

id. at 175. Mr. Aposhian filed a notice of appeal and sought an injunction pending appeal 

from this court, which was denied. Id. at 226. 
9 

II 

 We review the district court’s denial of a preliminary injunction for abuse of 

discretion. Wilderness Workshop v. BLM, 531 F.3d 1220, 1223 (10th Cir. 2008). “An 

abuse of discretion occurs ‘only when the trial court bases its decision on an erroneous 

conclusion of law or where there is no rational basis in the evidence for the ruling.’” 

Utah Licensed Beverage Ass’n v. Leavitt, 256 F.3d 1061, 1065 (10th Cir. 2001) (quoting 

Hawkins v. City and Cty. of Denver, 170 F.3d 1281, 1292 (10th Cir. 1999)). “Thus, we 

review the district court’s factual findings for clear error and its conclusions of law de 

novo.” Fish v. Kobach, 840 F.3d 710, 723 (10th Cir. 2016). 

 “A preliminary injunction is an extraordinary remedy, the exception rather than 

the rule.” United States ex rel. Citizen Band Potawatomi Indian Tribe v. Enter. Mgmt. 

Consultants, Inc., 883 F.2d 886, 888 (10th Cir. 1989). “To obtain a preliminary 

injunction, the movant must show: (1) a substantial likelihood of success on the merits; 

(2) irreparable harm to the movant if the injunction is denied; (3) the threatened injury 

outweighs the harms that the preliminary injunction may cause the opposing party; and 

(4) the injunction, if issued, will not adversely affect the public interest.” Gen. Motors 

Corp. v. Urban Gorilla, LLC, 500 F.3d 1222, 1226 (10th Cir. 2007). The third and fourth 

factors “merge” when, like here, the government is the opposing party. Nken v. Holder, 

556 U.S. 418, 435 (2009). “[B]ecause a preliminary injunction is an extraordinary 

remedy, the [movant’s] right to relief must be clear and unequivocal.” Dominion Video 

Satellite, Inc. v. Echostar Satellite Corp., 356 F.3d 1256, 1261 (10th Cir. 2004) (internal 

quotation marks omitted). 
10 

III 

 To obtain preliminary injunctive relief, Mr. Aposhian must demonstrate a 

substantial likelihood of success on the merits of his challenge to the Final Rule. While 

his complaint raises both constitutional and APA claims, he does not cite to any 

constitutional provision or section of the APA in the portion of his opening brief 

discussing his likelihood of success on the merits. It is clear, however, that Mr. 

Aposhian’s merits arguments in this court concern only issues of statutory interpretation. 

Specifically, he contends that he has demonstrated a substantial likelihood of success on 

the merits because ATF’s interpretation of 26 U.S.C. § 5845(b) contradicts the 

unambiguous language of the statute. Aplt. Br. at 13. He also argues that because the 

statute is unambiguous, ATF had no authority to promulgate a rule defining its terms. Id.

at 30. In the alternative, Mr. Aposhian contends that any ambiguity in the statute must be 

construed in his favor under the rule of lenity.4 Id. at 37.5

 

Because Mr. Aposhian is challenging ATF’s authority to promulgate the Final 

Rule, the APA governs our review. See WildEarth Guardians v. United States Fish and 

4

 Under the rule of lenity, courts “interpret ambiguous statutes . . . in favor of 

criminal defendants.” United States v. Gay, 240 F.3d 1222, 1232 (10th Cir. 2001). “The 

rule of lenity ‘is a rule of last resort [and] the mere assertion of an alternative 

interpretation is not sufficient to bring the rule into play.’” Id. (quoting United States v. 

Blake, 59 F.3d 138, 140 (10th Cir. 1995)). 

5

 Mr. Aposhian states in a footnote in his reply brief that his “claim is that the 

Final Rule was issued in violation of Articles I, § 1, I, §7, and II, § 3, on theories related 

to the vesting clauses, bicameralism and presentment, non-divestment and separation of 

powers principles.” Aplt. Rep. Br. at 27 n.1 (citing his complaint). Not only does Mr. 

Aposhian fail to cite any caselaw supporting these arguments, these constitutional 

theories are absent from his opening brief. We routinely “decline[] to consider arguments 
11 

Wildlife Serv., 784 F.3d 677, 683 (10th Cir. 2015) (noting that the APA applies “when 

asking whether an agency has acted within its authority”); see also Citizens’ Comm. to 

Save Our Canyons v. Krueger, 513 F.3d 1169, 1176 (10th Cir. 2008) (stating that the 

APA “governs judicial review of agency actions”). As relevant to the arguments here, we 

may only set aside agency action that is “in excess of statutory jurisdiction, authority, or 

limitations, or short of statutory right.” 5 U.S.C. § 706(2)(C). We conclude that Mr. 

Aposhian has not shown that ATF acted beyond its authority and has thereby failed to 

demonstrate a substantial likelihood of success under the APA. 

A 

At the outset, we must determine what standard we are to apply in addressing the 

Final Rule’s conclusion that bump stocks are “machineguns” under the statutory 

definition. When confronted with this question of statutory interpretation and what if any 

weight the district court should accord ATF’s interpretation under its Final Rule, the 

parties seemed oddly in agreement. Mr. Aposhian argued repeatedly against the 

application of Chevron deference, citing Chevron in his motion for a preliminary 

injunction to argue that ATF’s construction of the statute should be rejected, Aplt. App. 

at 44–45, and devoting the entirety of his reply brief to argue the Final Rule fails under 

both step one and step two of Chevron, see id. at 111–19. And, as the district court noted 

that are not raised, or are inadequately presented, in an appellant’s opening brief,” 

Bronson v. Swensen, 500 F.3d 1099, 1104 (10th Cir. 2007)), and it is well settled that we 

do not ordinarily review issues raised for the first time in a reply brief, Sylvia v. Wisler, 

875 F.3d 1307, 1332 n.7 (10th Cir. 2017). We see no reason to deviate from those 

principles here.
12 

in its memorandum opinion and order denying the motion for a preliminary injunction, 

the government “went out of [its] way to avoid citing Chevron and its progeny and 

repeatedly stressed that [the defendants] neither request, nor believe their interpretations 

are entitled to, any measure of deference.” Id. at 177 n.8. In the end, the district court 

did not apply the Chevron framework. Id. Rather, it concluded that the Final Rule 

represented the best interpretation of the statute. Id. at 181. 

Generally, however, “we apply the test established by Chevron . . . when asking 

whether an agency has acted within its authority.” WildEarth, 784 F.3d at 683 

(emphasizing that appellate review under APA § 706(2)(C) proceeds under the Chevron 

framework). If Chevron applies, we first ask if the statute is ambiguous concerning 

whether bump stocks can be considered “machineguns.” If so, we sustain the Final 

Rule’s conclusion that bump stocks are machine guns as long as the Final Rule’s 

conclusion is reasonable. See Entergy Corp. v. Riverkeeper, Inc., 556 U.S. 208, 218 

(2009). At this second step, an “agency need not adopt . . . the best reading of the statute, 

but merely one that is permissible.” Dada v. Mukasey, 554 U.S. 1, 29 n.1 (2008). On the 

other hand, if Chevron’s two-step framework is inapplicable, we accept ATF’s 

interpretation only if it is the best reading of the statute. While the parties protest the 

applicability of Chevron on various grounds, we conclude that the Final Rule warrants 

consideration under the Chevron framework. 

(i) 

Initially, the applicability of Chevron depends on what kind of rule the Final Rule 

represents. There is a “central distinction” under the APA between legislative rules and 
13 

interpretive rules. Chrysler Corp. v. Brown, 441 U.S. 281, 301 (1979); see 5 U.S.C. 

§ 553(b), (d). Legislative rules generally receive Chevron deference, whereas 

interpretive rules “enjoy no Chevron status as a class.” United States v. Mead Corp., 533 

U.S. 218, 232 (2001). 

A legislative rule is one that “is promulgated pursuant to a direct delegation of 

legislative power by Congress and . . . changes existing law, policy, or practice.” Rocky 

Mountain Helicopters, Inc. v. F.A.A., 971 F.2d 544, 546 (10th Cir. 1992). A legislative 

rule affects individual rights and obligations, and, if it is “the product of certain 

procedural requisites,” it has the force and effect of law. Chrysler Corp., 441 U.S. at 

301–02. An interpretive rule, on the other hand, “attempts to clarify an existing rule but 

does not change existing law, policy, or practice.” Rocky Mountain Helicopters, 971 

F.2d at 546–47. An interpretive rule simply “‘advise[s] the public of the agency’s 

construction of the statute and rules which it administers.’” Sorenson Commc’ns, Inc. v. 

F.C.C., 567 F.3d 1215, 1222 (10th Cir. 2009) (quoting Shalala v. Guernsey Mem. Hosp., 

514 U.S. 87, 99 (1995)). 

The government contends—and the district court found—that the Final Rule is 

merely interpretive. See Aple. Br. at 37–38; Aplt. App. at 176. But “[t]he agency’s own 

label for its action is not dispositive.” Sorenson, 567 F.3d at 1223. Instead, “[t]he court 

must rely upon the reasoning set forth in the administrative record and disregard post hoc

rationalizations of counsel.” Id. at 1221. Here, “[a]ll pertinent indicia of agency intent 

confirm that the [Final] Rule is a legislative rule.” Guedes v. Bur. of Alcohol, Tobacco, 
14 

Firearms & Explosives, 920 F.3d 1, 18 (D.C. Cir. 2019) (reviewing the Final Rule under 

the Chevron framework). 

First, the Final Rule demonstrates that ATF intended to change the legal rights and 

obligations of bump-stock owners. The Final Rule directed bump-stock owners to either 

destroy or surrender to ATF any bump stock in their possession and stated that “[t]he rule 

would criminalize only future conduct, not past possession of bump-stock-type devices 

that ceases by the effective date of this rule.” Final Rule at 66,525. The Final Rule 

announced that a person “in possession of a bump-stock-type device” in fact “is not 

acting unlawfully unless they fail to relinquish or destroy their device after the effective 

date of this regulation.” Id. at 66,523 (emphasis added). This effort to “‘directly 

govern[] the conduct of members of the public, affecting individual rights and 

obligations’” is “powerful evidence” that ATF intended the Final Rule to be a binding 

application of its rulemaking authority. Guedes, 930 F.3d at 18 (quoting Long Island 

Care at Home, Ltd. v. Coke, 551 U.S. 158, 172 (2007)). 

ATF, when promulgating the Final Rule, “further evinced its intent to exercise 

legislative authority by expressly invoking the Chevron framework and then elaborating 

at length as to how Chevron applies to the [Final] Rule.” Id. at 18–19 (noting that ATF’s 

“exegesis” on Chevron “would have served no purpose unless the agency intended the 

[Final] Rule to be legislative in character”). Moreover, the Final Rule expressly invoked 

two separate delegations of legislative power, one under the NFA, 26 U.S.C. § 7805, and 

one under the GCA, 18 U.S.C. § 926(a). See Final Rule at 66,515. These provisions, 
15 

according to the Final Rule, give the Attorney General “the responsibility for 

administering and enforcing the NFA and GCA,” which he has delegated to ATF. Id.

In addition, the Final Rule was published in the Code of Federal Regulations 

(CFR). By statute, administrative rules published in the CFR are limited to those “having 

general applicability and legal effect.” 44 U.S.C. § 1510. For all of these reasons, it is 

evident that the Final Rule intends to speak with the force of law. 

Ordinarily, legislative rules are entitled to Chevron deference. See Sinclair 

Wyoming Refining Co. v. EPA, 887 F.3d 986, 991 (10th Cir. 2017). Nonetheless, the 

parties assert that Chevron deference is inappropriate here. Mr. Aposhian argues that 

Chevron deference has been waived by the government because the government has 

disavowed any reliance on Chevron throughout this litigation. Aplt. Br. at 42–43. Next, 

the parties (including the government) submit that Chevron deference is inapplicable 

when the government interprets a statute that imposes criminal liability. See Aplt. Br. at 

44; Aple. Br. at 40. Neither of these objections to applying Chevron are likely to succeed 

in the context of the Final Rule, particularly when one recalls the citation to and reliance 

on Chevron when the Final Rule was promulgated. 

(ii) 

Mr. Aposhian relies on our decision in Hydro Resources, Inc. v. EPA, 608 F.3d 

1131 (10th Cir. 2010), to argue that the government has waived any reliance on Chevron 

deference and that we must abide by that waiver. Aplt. Br. at 42, 43. In Hydro 

Resources, we reviewed de novo the Environmental Protection Agency’s interpretation of 

a statute because “throughout the proceedings before the panel and . . . the en banc court, 
16 

[the agency] itself ha[d]n’t claimed any entitlement to deference.” Id. at 1146. We noted 

that “[i]n these circumstances, when the agency doesn’t ask for deference to its statutory 

interpretation, ‘we need not resolve the . . . issues regarding deference which would be 

lurking in other circumstances.’” Id. (emphasis added) (quoting Estate of Cowart v. 

Nicklos Drilling Co., 505 U.S. 469, 477 (1992)). However, this passage should not be 

read as prohibiting our application of Chevron merely on the agency’s say so. Simply 

put, “need not” does not mean “may not.” Moreover, Hydro Resources did not address a 

scenario where, like here, a party other than the government invokes the Chevron 

framework. 

We addressed this specific scenario in TransAm Trucking, Inc. v. Admin. Review 

Bd., 833 F.3d 1206, 1212 n.4 (10th Cir. 2016), and held that the Chevron framework 

applies, including deference at Chevron step two. The dissent in TransAm criticized the 

majority for making “a wholly uninvited foray into step two of Chevron land,” id. at 1216 

(Gorsuch, J., dissenting), because “the only party to mention Chevron . . . was [the 

plaintiff], and then only in a footnote in its brief and then only as part of an argument that 

the statute is not ambiguous,” id. (emphasis in original). The majority nonetheless 

applied both steps of Chevron and gave the agency’s interpretation of the statute 

deference, id. at 1212, defending its application of Chevron deference by stating, “We 

received our invitation from TransAm [to apply the Chevron framework] in its opening 

brief . . . TransAm, the appellant in this matter, relied on Chevron to argue the [agency’s] 

construction of the [statute] should be rejected.” Id. at n.4. 
17 

This case is akin to TransAm. While the government has declined to invoke 

Chevron throughout the course of this litigation, see Aple. Br. at 16 (arguing that 

“plaintiff’s discussion of Chevron deference has no bearing on the disposition of this 

suit”), Mr. Aposhian, like the plaintiff in TransAm, relies on Chevron in his opening brief 

to argue that ATF’s construction of the statute should be rejected. In contending that 

ATF’s interpretation “contradicts the statute itself,” Aplt. Br. at 13 (capitalization 

omitted), Mr. Aposhian cites Chevron, arguing that the inquiry is whether the statute 

“‘has directly spoken to the precise question at issue,’ and, if so, ‘that is the end of the 

matter; for the court as well as the agency must give effect to the unambiguously 

expressed intent of Congress,’” id. at 14 (quoting Chevron, 467 U.S. at 842–43). The 

plaintiff in TransAm likewise cited Chevron “as part of an argument that the statute is not 

ambiguous” (Chevron step one), 833 F.3d at 1216 (Gorsuch, J., dissenting), yet the 

majority still concluded that the plaintiff provided an “invitation” to apply both steps of 

the Chevron framework, id. at 1212 n.4. Our “invitation” to apply the Chevron

framework in this case is even clearer than in TransAm, given that Mr. Aposhian (1) cites 

Chevron in the text of his opening brief rather than in a footnote; and (2) relied on 

Chevron in his motion for a preliminary injunction at the district court, Aplt. App. at 44–

45, and in his motion for an injunction pending appeal, id. at 150. Because Mr. Aposhian 

has invoked Chevron throughout the course of this litigation, his objection to Chevron 

deference based on the government’s waiver is unlikely to succeed.6

6

 While Mr. Aposhian has clearly presented an “invitation” to apply the Chevron

framework under TransAm, we note that our cases are not entirely consistent as to 
18 

(iii) 

 Next, the parties contend that Chevron deference is inapplicable where the 

government interprets a statute that imposes criminal liability. See Aplt. Br. at 44 

(“‘[C]riminal laws are for courts, not for the Government, to construe.’”) (quoting 

Abramski v. United States, 573 U.S. 169, 191 (2014)); Aple. Br. at 40 (same). According 

to Mr. Aposhian, “ATF’s rejection of deference in favor of the rule of lenity” is required 

by our precedent and constitutional limitations. Aplt. Br. at 44. Mr. Aposhian also relies 

on United States v. Apel, 571 U.S. 359, 369 (2014), for the proposition that “we have 

never held that the Government’s reading of a criminal statute is entitled to any 

deference.” Mr. Aposhian, however, has failed to demonstrate a likelihood of success in 

establishing a general rule against applying Chevron to agency interpretations of statutes 

with criminal law implications. Rather, controlling precedent points in the other 

direction. 

 In Babbitt v. Sweet Home Chapter of Communities for a Great Oregon, 515 U.S. 

687 (1995), the Supreme Court reviewed a regulation interpreting a term in the 

whether such an invitation is necessary. Compare Am. Wild Horse Pres. Campaign v. 

Jewell, 847 F.3d 1174, 1187 (10th Cir. 2016) (describing Chevron as a “two-part 

standard of review”) (emphasis added), with Hays Med. Ctr. v. Azar, --- F.3d ---, No. 17-

3232, 2020 WL 1922595, at *13 n.18 (10th Cir. Apr. 21, 2020) (concluding that Chevron 

can be waived where, unlike here, its “invocation” is merely “perfunctory and fleeting”). 

To the extent that Chevron is a standard of review, we would need no invitation to apply 

it. See Gardner v. Galetka, 568 F.3d 862, 879 (10th Cir. 2009) (“It is one thing to allow 

parties to forfeit claims, defenses, or lines of argument; it would be quite another to allow 

parties to stipulate or bind us to application of an incorrect legal standard . . . .”); see also 

Guedes, 920 F.3d at 22 (“The ‘independent power’ to identify and apply the correct law 

presumably includes application of the Chevron framework when determining the 

meaning of a statute.”). 
19 

Endangered Species Act (ESA), which, like the regulation in this case, carried both civil 

and criminal implications. The challengers argued that Chevron deference was 

inappropriate because the ESA included criminal penalties. See id. at 704 n.18. The 

Court disagreed, holding that it would defer “to the Secretary’s reasonable interpretation” 

under Chevron. Id. at 703–04. 

 Babbitt also rejected the argument “that the rule of lenity should foreclose any 

deference to the [agency’s] interpretation of the [statute] because the statute includes 

criminal penalties.” Id. at 704 n.18. The Court reasoned, 

The rule of lenity is premised on two ideas: First, “‘a fair 

warning should be given to the world in language that the 

common world will understand, of what the law intends to do 

if a certain line is passed’”; second, “legislatures and not 

courts should define criminal activity.” We have applied the 

rule of lenity in a case raising a narrow question concerning 

the application of a statute that contains criminal sanctions to 

a specific factual dispute—whether pistols with short barrels 

and attachable shoulder stocks are short-barreled rifles—

where no regulation was present. See United States v. 

Thompson/Center Arms Co., 504 U.S. 505, 517–518, and n. 9, 

(1992). We have never suggested that the rule of lenity should 

provide the standard for reviewing facial challenges to 

administrative regulations whenever the governing statute 

authorizes criminal enforcement. 

Id. (emphasis added) (citation omitted). Thus, as in this case, where a regulation is at 

issue, and the agency (here, ATF) has both civil and criminal enforcement authority,

Babbitt suggests that Chevron, not the rule of lenity, should apply. 

 Our circuit precedent is in accord. In NLRB v. Oklahoma Fixture Co., 332 F.3d 

1284, 1287 (10th Cir. 2003) (en banc), we noted that “it is not entirely clear exactly how 

the Chevron analysis is affected by the presence of criminal liability in a statute being 
20 

interpreted by an agency.” Nonetheless, we concluded that, under Babbitt, it was 

appropriate to give “some deference” under Chevron to the National Labor Relations 

Board’s interpretation of an exception to a criminal prohibition on employer payments to 

labor organizations in the Labor Management Reporting Act. Id. (noting that “the degree 

of deference may be dependent upon considerations of the agency’s particular expertise 

and the policies implicated by the criminal statute in question, as well as the extent to 

which Congress has charged the agency with administering the criminal statute”). 

Accordingly, we looked at whether the agency’s interpretation was “a reasonable or 

permissible one” and was “not in conflict with interpretive norms regarding criminal 

statutes.” Id. & n.5 (stating that “criminal statutes must be construed narrowly, and that 

exceptions to those statutes must be construed broadly”). We concluded that the 

agency’s interpretation was reasonable and gave deference to its interpretation of the 

“criminal provision” at issue.7

 Id. at 1287, 1291. And contrary to Mr. Aposhian’s 

assertion, the majority in Oklahoma Fixture did not apply, or even mention, the rule of 

lenity. See id. at 1287–90. 

 We later gave deference under Chevron to a “reasonable” ATF regulation 

interpreting 18 U.S.C. § 922(g), despite the “criminal nature of that statute.” United 

States v. Atandi, 376 F.3d 1186, 1189 (10th Cir. 2004) (stating that “we unquestionably 

owe ‘some deference’ to the ATF’s regulation”) (quoting Okla. Fixture, 332 F.3d at 

7

 Notably, in contrast with the regulation in Babbitt and the regulation at issue 

here, the NLRB’s interpretation in Oklahoma Fixture carried only criminal implications. 

332 F.3d at 1291 n.1. (Briscoe, J., concurring). 
21 

1286–87, and citing Babbitt, 515 U.S. at 703). We emphasized that, as in this case, ATF 

“had been delegated authority to implement” § 922 by virtue of 18 U.S.C. § 926(a), id. 

(noting that § 926(a) “authoriz[es] ‘such rules and regulations as are necessary to carry 

out the provisions of this chapter’”), and we again did not invoke the rule of lenity. See 

id.8

 

We once again gave deference under Chevron to an agency’s interpretation of a 

statute with criminal implications in United States v. Hubenka, 438 F.3d 1026, 1032–34 

(10th Cir. 2006). In Hubenka, a jury found the defendant guilty of violating the Clean 

Water Act, and the defendant contended that “his activities . . . l[ay] beyond the reach of 

the [statute]” as interpreted by the Army Corps of Engineers. Id. at 1028. We 

nonetheless applied the Chevron framework and did not invoke the rule of lenity. Id. at 

1031 (“When a case involves an agency’s interpretation of a statute it administers, this 

court uses the two-step approach announced in Chevron . . . .”). We held that the Army 

Corps of Engineers’ “tributary rule [was] a permissible interpretation of the [statute].” 

Id. at 1034. Therefore, we stated that, “under Chevron, we must defer to the Corps’ 

interpretation of the statute” despite the criminal implications of the rule. Id. at 1034 

(affirming the defendant’s conviction). In sum, this court has repeatedly given agency 

interpretations with criminal law implications deference. 

8

 In York v. Secretary of the Treasury, 774 F.2d 417, 419 (10th Cir. 1985), we 

recognized ATF’s “enforcement power” under 26 U.S.C. § 7805(a) “to interpret 26 

U.S.C. § 5845(b),” the statute at issue in this case, “which provides that a ‘machine gun’ 

includes ‘any weapon which shoots, is designed to shoot, or can be readily restored to 

shoot, automatically more than one shot, without manual reloading, by a single function 

of the trigger.’” 
22 

 To be sure, the Supreme Court has recently “signaled some wariness about 

deferring to the government’s interpretations of criminal statutes.” Guedes, 920 F.3d at 

25 (citing Abramski, 573 U.S. at 191, and Apel, 571 U.S. at 369). But as the D.C. Circuit 

explained in Guedes, those statements “were made outside the context of a Chevroneligible interpretation.” Id. Specifically, 

[i]n Abramski, the Court declined to extend deference to 

informal guidance documents published by [ATF]. See 573 

U.S. at 191. And in Apel, the Court declined to defer to an 

interpretation contained in “Executive Branch documents” 

that were “not intended to be binding.” 571 U.S. at 368. 

When directly faced with the question of Chevron’s 

applicability to an agency’s interpretation of a statute with 

criminal applications through a full-dress regulation, the 

Court adhered to Chevron. See Babbitt, 515 U.S. at 704 n.18. 

Id. (emphasis added). Babbitt and our court’s precedents govern here, where ATF has 

promulgated a regulation through formal notice-and-comment proceedings. Under those 

precedents, Mr. Aposhian has failed to demonstrate a likelihood of success in establishing 

a rule against deference to agency interpretations with criminal law implications. 

B 

Because the precedents cited call for the application of Chevron, we now examine 

the Final Rule under Chevron. We first ask whether the agency-administered statute is 

ambiguous on the “precise question at issue.” Chevron, 467 U.S. at 842. If the statute’s 

meaning is unambiguous, then we need go no further. If we find ambiguity, our caselaw 

instructs us to proceed to Chevron’s second step and ask whether the agency has provided 

a “permissible construction” of the statute. Id. at 843. There, “the task that confronts us 

is to decide, not whether [the agency’s interpretation is] the best interpretation of the 
23 

statute, but whether it represents a reasonable one.” Atl. Mut. Ins. Co. v. Comm’r, 523 

U.S. 382, 389 (1998).

The NFA and GCA both define “machinegun” to mean “any weapon which 

shoots, is designed to shoot, or can be readily restored to shoot, automatically more than 

one shot, without manual reloading, by a single function of the trigger.” 26 U.S.C. 

§ 5845(b); see 18 U.S.C. § 921(a)(23). The definition of “machinegun” also includes 

“any part designed and intended solely and exclusively, or combination of parts designed 

and intended, for use in converting a weapon into a machinegun, and any combination of 

parts from which a machinegun can be assembled if such parts are in the possession or 

under the control of a person.” 26 U.S.C. § 5845(b). 

The Final Rule determines that semiautomatic rifles equipped with bump stocks 

are “machineguns” because they “function[ ] as the result of a self-acting or selfregulating mechanism that allows the firing of multiple rounds” through “a single pull of 

the trigger.” Final Rule at 66,553. Applying Chevron, the statutory definition of 

“machinegun” is ambiguous, and ATF’s interpretation is reasonable. Mr. Aposhian 

therefore is unlikely to succeed on the merits of his challenge to the Final Rule. 

(i) 

For the first step, to ascertain whether Congress clearly stated its intent on the 

precise statutory question at issue, courts should “apply[] the ordinary tools of statutory 

construction.” City of Arlington v. FCC, 569 U.S. 290, 296 (2013). “These tools include 

examination of the statute’s text, structure, purpose, history, and relationship to other 

statutes.” Harbert v. Healthcare Servs. Grp., Inc., 391 F.3d 1140, 1147 (10th Cir. 2004). 
24 

“Ambiguity is a creature not of definitional possibilities but of statutory context.” Brown 

v. Gardner, 513 U.S. 115, 118 (1994). Under this analysis, we agree with the D.C. 

Circuit that two features of the statutory definition of “machinegun” render it ambiguous. 

The first is the phrase “single function of the trigger,” and the second is the word 

“automatically.” Guedes, 920 F.3d at 29. 

“Single Function of the Trigger” 

 When applied to bump stocks, the statutory definition of machine gun is 

ambiguous with respect to the phrase “single function of the trigger.” That is because, 

within the statutory context, the phrase can have more than one meaning. See id. (“[T]he 

statutory phrase ‘single function of the trigger’ admits of more than one interpretation.”). 

Mr. Aposhian defines the phrase to mean a mechanical act of the trigger. Aplt. Br. at 26 

(arguing that “[c]ourts have emphasized that a trigger’s function is defined by how it 

mechanically operates, not by how the shooter engages it”). The government (and ATF), 

however, define “single function of the trigger” as “single pull of the trigger,” Aple. Br. 

at 14, which “considers the external impetus for the mechanical process.” Gun Owners of 

Am. v. Barr, 363 F. Supp. 3d 823, 832 (finding “the statutory definition of machine gun” 

to be “ambiguous with respect to the phrase ‘single function of the trigger’”).9

 

9

 The dissent states that ATF’s interpretation of “single function of the trigger” to 

mean “single pull of the trigger” refers only to the action of the trigger and not the 

volitional action of the shooter. Dissent at 7. The parties argue otherwise. Specifically, 

Mr. Aposhian and the government agree that ATF’s interpretation refers to the action of 

the shooter’s trigger finger. See Aplt. Br. at 25 (arguing that the Final Rule conflicts with 

the statute because it redefines “single function of the trigger” to mean only the 

“deliberate and volitional act of the user pulling the trigger”) (quotations omitted); Aple. 

Br. at 20 (arguing that the statute “is concerned with the shooter’s act of pulling the 
25 

 As the D.C. Circuit explained, 

The first interpretation would tend to exclude bump-stock 

devices: while a semiautomatic rifle outfitted with a bump 

stock enables a continuous, high-speed rate of fire, it does so 

by engendering a rapid bumping of the trigger against the 

shooter’s stationary finger, such that each bullet is fired 

because of a distinct mechanical act of the trigger. The 

second interpretation would tend to include bump-stock 

devices: the shooter engages in a single pull of the trigger 

with her trigger finger, and that action, via the operation of 

the bump stock, yields a continuous stream of fire as long she 

keeps her finger stationary and does not release it. 

Guedes, 920 F.3d at 29. 

 Within the statutory context, the phrase could have either meaning. The word 

“function” focuses on the “mode of action,” 4 Oxford English Dictionary 602 (1933), or 

“natural . . . action,” Webster’s New International Dictionary 876 (1933), by which the 

trigger operates. But that definition begs the question of whether “function” requires our 

focus upon the movement of the trigger, or the movement of the trigger finger. The 

statute is silent in this regard. “In light of those competing, available interpretations, the 

statute contains a ‘gap for the agency to fill.’” Guedes, 920 F.3d at 29 (quoting Chevron, 

467 U.S. at 843). 

 Mr. Aposhian argues that “single function of the trigger” plainly means a 

mechanical movement of the trigger, asserting that Congress understood when it enacted 

trigger”) (emphasis added). Because the parties do not argue that ATF’s interpretation 

refers to the action of the trigger, that argument is waived. See Wyoming v. Livingston, 

443 F.3d 1211, 1216 (10th Cir. 2006). We acknowledge the parties’ agreement on this 

issue, not to support our conclusion that the statute is ambiguous, but rather to explain 

why we do not address the argument that is the focus of the dissent. 
26 

the NFA that there was a “difference in the internal mechanism that allowed a 

machinegun to fire multiple rounds continuously with one function of the trigger and a 

semiautomatic weapon, which fires only one round with each function of the trigger.” 

Aplt. Br. at 36. But this distinction in no way requires a “function” to be a mechanical 

action. In fact, the definition Congress gave to the term “semiautomatic rifle” in the 

GCA is “any repeating rifle which utilizes a portion of the energy of a firing cartridge to 

extract the fired cartridge case and chamber the next round, and which requires a separate

pull of the trigger to fire each cartridge.” 18 U.S.C. § 921(a)(28) (emphasis added). We 

conclude the statutory definition of machine gun is ambiguous with respect to the phrase 

“single function of the trigger.” 

“Automatically” 

Similarly, the statutory term “automatically” is ambiguous when applied to bump 

stocks. In the statute, “automatically” functions as an adverb modifying the verb 

“shoots.” Relying on definitions from the 1930s, the government and the Final Rule 

interpret the word to mean “the result of a self-acting or self-regulating mechanism.” 

Final Rule at 66,519. Mr. Aposhian counters that because the shooter must maintain 

constant rearward pressure on the extension ledge with the trigger finger and constant 

forward pressure with the non-trigger hand for the bump stock to work, a bump stock 

cannot shoot “automatically.” Aplt. Br. at 22–23. Essentially, “the parties’ dispute is 

whether the . . . pressure exerted by the shooter . . . requires the conclusion that a bump 

stock does not shoot automatically.” Gun Owners, 363 F. Supp. 3d at 831. 
27 

 The statutory text does not answer this question. The term “automatically,” 

however, does not require there be no human involvement to give rise to “more than one 

shot.” Webster’s New International Dictionary provides that “automatically” is the 

adverbial form of “automatic,” meaning “[h]aving a self-acting or self-regulating 

mechanism that performs a required act at a predetermined point in an operation.” 

Webster’s New International Dictionary 187 (2d ed. 1934) (emphasis added); see also

Webster’s New International Dictionary 156 (1933) (defining “automatic” as “self-acting 

or self-regulating,” especially applied to “machinery or devices which perform parts of 

the work formerly or usually done by hand”) (emphasis added). Similarly, the Oxford 

English Dictionary defines the term to mean “[s]elf-acting under conditions fixed for it, 

going of itself.” 1 Oxford English Dictionary 574 (1933) (emphasis added). Therefore, 

under its ordinary meaning, the term can be read to permit limited human involvement to 

bring about “more than one shot.” As the D.C. Circuit explained, 

[A] quite common feature of weapons that indisputably 

qualify as machine guns is that they require both a single pull 

of the trigger and the application of constant and continuing 

pressure on the trigger after it is pulled. We know, therefore, 

that the requirement of some measure of additional human 

input does not render a weapon nonautomatic. 

Guedes, 920 F.3d at 30 (emphasis in original) (citation omitted). But how much human 

input is too much? The statute does not say. 

 Mr. Aposhian cites Staples v. United States, 511 U.S. 600, 602 n.1 (1994), for the 

proposition that the shooter’s manual manipulations of the weapon clearly do not meet 

the definition of “automatically.” See Aplt. Br. at 18, 21. Reliance on Staples is 
28 

misplaced. Staples concerned the necessary mens rea element for a conviction for 

possession of an unregistered machine gun under the NFA. 511 U.S. at 604. At the 

beginning of the opinion, the Court provided a footnote explaining how it was using 

certain terms in the opinion, including “automatic” and “semi-automatic.” Id. at 602 n.1. 

It stated, 

[a]s used here, the terms “automatic” and “fully automatic” 

refer to a weapon that fires repeatedly with a single pull of the 

trigger. That is, once its trigger is depressed, the weapon will 

automatically continue to fire until its trigger is released or 

the ammunition is exhausted. Such weapons are 

“machineguns” within the meaning of the Act. We use the 

term “semiautomatic” to designate a weapon that fires only 

one shot with each pull of the trigger, and which requires no 

manual manipulation by the operator to place another round 

in the chamber after each round is fired. 

Id. (emphasis added). 

As the Seventh Circuit explained in United States v. Olofson, 563 F.3d 652, 657 

(7th Cir. 2009), the statutory definition of these terms was not at issue in Staples, and the 

Court was not purporting to interpret the statute. Instead, “the Court simply was 

providing a glossary for terms frequently appearing in the opinion.” Id. Moreover, the 

Court did not suggest that “automatic” firing excluded all “manual manipulation” of the 

gun, as Mr. Aposhian maintains. The Court mentioned “manual manipulation” only in 

connection with placing another round in the chamber. Staples, 511 U.S. at 602 n.1. 

Precluding “manual manipulation” to put another round in the chamber is not inconsistent 

with the statutory definition of a machine gun, which shoots more than one shot “without 

manual reloading,” 26 U.S.C. § 5845(b). 
29 

In sum, the statutory definition of machine gun contains two central ambiguities, 

both of which ATF has attempted to resolve. Accordingly, we proceed to Chevron’s 

second step. 

(ii) 

When, as here, Congress leaves an implicit statutory gap, we ask at step two 

“whether the [regulation] is based on a permissible construction of the statute.” Chevron, 

467 U.S. at 843. “‘[T]he agency’s interpretation need not be the only one it could have 

adopted, or the one that this court would have reached had the question initially arisen in 

a judicial proceeding.’” Anderson v. Dep’t of Labor, 422 F.3d 1155, 1181 (10th Cir. 

2005) (quoting Salt Lake City v. W. Area Power Admin., 926 F.2d 974, 978 (10th Cir. 

1991)). 

ATF’s interpretation of “single function of the trigger” to mean “single pull of the 

trigger” is a permissible reading of the statute. See Guedes, 920 F.3d at 31 (concluding 

ATF’s interpretation of “single function of the trigger” is permissible); Gun Owners, 363 

F. Supp. 3d at 832 (same). ATF’s interpretation accords with how some courts have read 

the statute. For example, in Akins, the Eleventh Circuit held that ATF’s reading of 

“single function of the trigger” to mean “single pull of the trigger” was “consonant with 

the statute and its legislative history.” 312 F. App’x at 200 (concluding that the Akins 

Accelerator, a type of bump stock, was reasonably classified as a machine gun). In 

addition, the Final Rule’s interpretation “accords with how the phrase ‘single pull of the 

trigger’ was understood at the time of the enactment of the [NFA].” Guedes, 920 F.3d at 

31. The Final Rule cites a congressional hearing for the NFA where the then-president of 
30 

the National Rifle Association testified that the term “machine gun” included any firearm 

“capable of firing more than one shot by a single pull of the trigger, a single function of 

the trigger.” Final Rule at 66,518 (emphasis added). Further, the House Report 

accompanying the bill that eventually became the NFA states that the bill “contains the 

usual definition of a machine gun as a weapon designed to shoot more than one shot . . . 

by a single pull of the trigger.” H.R. Rep. No. 73-1780, at 2 (1934) (emphasis added). 

Nonetheless, the dissent states that if the Final Rule does refer to the motion of the 

trigger finger—a proposition the parties do not dispute—then the regulation is invalid as 

being broader than the unambiguous NFA. Dissent at 8 n.3. This assertion is contrary to 

authority in this circuit. Specifically, this court has looked to a shooter’s volitional 

actions to determine whether automation was obtained with a “single function of the 

trigger” under the NFA. See United States v. Oakes, 564 F.2d 384, 388 (10th Cir. 1977). 

In Oakes, we held that a “gun was a machine gun within the [NFA’s] statutory definition” 

because “the shooter could, by fully pulling the trigger . . . obtain automation with a 

single trigger function.” Id. (emphasis added). Thus, rather than being broader than the 

NFA, ATF’s interpretation of “single function of the trigger” accords with how this court 

has interpreted the statute. 

ATF’s interpretation of “automatically” is likewise permissible. The Final Rule’s 

“definition accords with the everyday understanding of the word ‘automatic.’” Guedes, 

920 F.3d at 31. That is, the bump stock “performs a required act at a predetermined 

point” in the firing sequence by directing the recoil energy into the space created by the 

sliding stock. The bump stock is also “self-acting under conditions fixed for it.” The 
31 

shooter’s positioning of the trigger finger on the extension ledge and application of 

forward pressure on the front of the gun provide the conditions necessary for the bump 

stock to repeatedly perform its purpose: to eliminate the need for the shooter to manually 

capture the recoil energy to fire additional rounds. We therefore disagree with the 

dissent’s contention that a bump stock cannot be “automatic” because it will not work 

without constant forward pressure. Dissent at 12. The bump stock performs part of the 

work usually done by hand at a predetermined point in the operation, under conditions 

fixed for it by the shooter. 

In addition, ATF’s interpretation focuses the inquiry about what needs to be 

automated precisely where the statute does: the ability of the trigger function to produce 

“more than one shot, without manual reloading.” 26 U.S.C. § 5845(b); see Guedes, 920 

F.3d at 31–32. Further, ATF’s interpretation tracks the interpretation reached by the 

Seventh Circuit, where the court interpreted the term to require a “self-acting 

mechanism” without requiring more. Olofson, 563 F.3d at 658; see also Guedes, 920 

F.3d at 32; Gun Owners, 363 F. Supp. 3d at 832 (holding that ATF’s “interpretation [of 

the term ‘automatically’] is consistent with judicial interpretations of the statute”). 

Because ATF’s Final Rule sets forth a reasonable interpretation of the statute’s 

ambiguous definition of “machinegun,” it merits our deference. Mr. Aposhian has not 

demonstrated a likelihood of success on the merits of his challenge to the Final Rule. 

IV 

 Although we could affirm the district court’s denial of preliminary injunctive 

relief solely on the ground that Mr. Aposhian has failed to demonstrate a substantial 
32 

likelihood of success on the merits, we also conclude that Mr. Aposhian has not met the 

other prerequisites for preliminary relief. 

Irreparable Harm 

 At the district court, “[t]he parties [did] not dispute that Mr. Aposhian will 

experience irreparable harm if the injunction is denied.” Aplt. App. at 175. They did 

“disagree about what that irreparable harm is.” Id. at n.4. Mr. Aposhian argued only that 

he would “be harmed by being forced to comply with a rule that has been promulgated in 

contravention of constitutional principles of separation-of-powers.” Id. The government 

conceded only that the irreparable harm was the loss of Mr. Aposhian’s bump stock. Id. 

On appeal, Mr. Aposhian again contends that he will suffer irreparable harm 

because the Final Rule was issued in violation of his constitutional rights—specifically, 

the separation of powers doctrine. Aplt. Br. at 48. The government now asserts that Mr. 

Aposhian will not suffer irreparable harm, contending that there is no support for the 

proposition that a generalized separation-of-powers violation constitutes irreparable 

harm. Aple. Br. at 44. We agree with the government that Mr. Aposhian has not met his 

burden of demonstrating irreparable harm. 

Mr. Aposhian relies on our holding in Free the Nipple-Fort Collins v. City of Fort 

Collins, 916 F.3d 792, 806 (10th Cir. 2019), where we held that “[w]hat makes an injury 

‘irreparable’ is the inadequacy of, and the difficulty of calculating, a monetary remedy 

after a full trial.” We noted that “[a]ny deprivation of any constitutional right fits that 

bill.” Id. But in the merits portion of his opening brief, Mr. Aposhian does not cite to a 

single constitutional provision or rely on any constitutional theory to argue that the Final 
33 

Rule is invalid; rather, his arguments focus on whether the Final Rule contradicts the 

statute.10 We cannot conclude that Mr. Aposhian has shown irreparable harm based on 

the deprivation of a constitutional right when he does not even raise a constitutional 

challenge to the Final Rule in this court. 

Even if Mr. Aposhian had properly raised a constitutional argument, he has not 

cited a single case where a generalized separation of powers, by itself, constituted 

irreparable harm. To the contrary, our cases finding that a violation of a constitutional 

right alone constitutes irreparable harm are limited to cases involving individual rights, 

not the allocation of powers among the branches of government. See, e.g., Free the 

Nipple, 916 F.3d at 806 (alleged equal protection violation); Awad v. Ziriax, 670 F.3d 

1111, 1119 (10th Cir. 2012) (alleged First Amendment violation); see generally 11A 

Charles Alan Wright, Arthur R. Miller & Mary Kay Kane, FED. PRAC. & PROC. § 2948.1 

(3d ed. 2019) (“When an alleged deprivation of a constitutional right is involved, such as 

the right to free speech or freedom of religion, most courts hold that no further showing 

of irreparable harm is necessary.”) (emphasis added). For these reasons, he has not met 

his burden of demonstrating that he would suffer irreparable harm absent an injunction. 

The dissent asserts that the government has waived any argument as to irreparable 

harm by conceding in the district court that Mr. Aposhian would suffer irreparable harm. 

Our precedent says otherwise. For instance, in Dominion, the parties stipulated in a 

contract that a breach of an exclusivity provision would give rise to irreparable harm and 

10 As noted, the constitutional arguments Mr. Aposhian raised for the first time in 

a footnote in his reply brief are waived. Sylvia, 875 F.3d at 1332 n.7. 
34 

warrant injunctive relief. 356 F.3d at 1261. The district court relied solely on the parties’ 

stipulation to find that the plaintiff had met its burden of demonstrating irreparable harm. 

Id. at 1266. We reversed, concluding that the “stipulation without more is insufficient to 

support an irreparable harm finding.” Id. The same holds true here. 

We emphasize that it is Mr. Aposhian’s burden to demonstrate irreparable harm. 

Awad, 670 F.3d at 1128 n.14 (noting that the plaintiff has the “burden under [each of] the 

four preliminary injunction factors”). While the government stated in the district court 

that the loss of Mr. Aposhian’s bump stock would constitute irreparable harm, Mr. 

Aposhian has never made a loss-of-property argument. Therefore, he has waived this 

argument and cannot rely on it to satisfy his burden.11

Harm to the Government and the Public Interest 

 Mr. Aposhian has also failed to meet the remaining prerequisites for a preliminary 

injunction. Specifically, he has not shown that the threatened injury outweighs the harms 

that the preliminary injunction will cause the government or that the injunction, if issued, 

will not adversely affect the public interest. These factors “merge” when the government 

is the opposing party. Nken, 556 U.S. at 435. 

 Mr. Aposhian argues that the “balance of equities” favors an injunction, stating 

that the public interest weighs in his favor because the public has an interest in protecting 

11 In any event, we note that the loss of a bump stock cannot constitute irreparable 

harm because Mr. Aposhian could be awarded compensatory damages. See Salt Lake 

Tribune Pub. Co., LLC v. AT&T Corp., 320 F.3d 1081, 1105 (10th Cir. 2003) 

(“Irreparable harm, as the name suggests, is harm that cannot be undone, such as by an 

award of compensatory damages or otherwise.”).
35 

an individual’s constitutional rights. Aplt. Br. at 49–50. But Mr. Aposhian has not 

argued that the Final Rule violates an individual constitutional right. Moreover, the 

public has a strong interest in banning the possession and transfer of machine guns, 

including bump stocks. The ban supports the safety of the public in general, see Final 

Rule at 66,515, and the safety of law enforcement officers and first responders, id. at 

66,551. 

 Mr. Aposhian counters that because he is a law-abiding citizen, “ATF cannot 

plausibly suggest that public safety demands that he be deprived of his device any 

longer.” Aplt. Br. at 50. The government’s general public safety concerns, however, still 

apply to Mr. Aposhian. Congress has prohibited Mr. Aposhian, no less than any other 

individual, from owning a bump stock. See Gun Owners, 363 F. Supp. 3d at 834 

(“Congress restricts access to machine guns because of the threat the weapons pose to 

public safety . . . All of the public is at risk, including the smaller number of bump stock 

owners.”). We conclude, and the dissent does not disagree, that Mr. Aposhian has failed 

to demonstrate that the threatened injury to him outweighs the harm that the preliminary 

injunction may cause to the government or that the injunction will not adversely affect 

the public interest. 

V 

 For the foregoing reasons, we affirm the district court’s denial of a preliminary 

injunction. 
Aposhian v. Barr, et al., 19-4036 

CARSON, J., dissenting.

In our Republic, Congress has the power to make and change laws. U.S. Const. 

art. I. Yet that preferred route often takes a back seat to a more expedient one. As is now 

often the case, the Executive Branch steps in and seeks to remedy an unpopular or poorly 

drafted law through an administrative regulation. And to be sure, the Executive can do so 

when the law is ambiguous; the Supreme Court has made as much clear. Chevron, 

U.S.A., Inc. v. Nat. Res. Def. Counsel, 467 U.S. 837 (1984). 

But regardless of the Executive’s ability to repair ambiguous laws, unambiguous

laws—no matter how problematic or out of favor—are out of its reach. See Epic Sys. 

Corp. v. Lewis, 138 S. Ct. 1612, 1630 (2018) (explaining that Chevron deference is 

unwarranted when “traditional tool[s] of statutory construction” are “up to the job of 

solving [a statute’s] interpretive puzzle”); Big Horn Coal Co. v. Sadler, 924 F.3d 1317, 

1322 (10th Cir. 2019) (“[I]f Congress has spoken ‘directly’ to the ‘precise question at 

issue,’ the inquiry ends, and we must give effect to the express intent of Congress.” 

(quoting Chevron, 476 U.S. at 842)). Thus, when a party challenges a regulation that 

implements an unambiguous law in court, the Judiciary must be mindful that neither it 

nor the Executive has the power to make the law. See Sessions v. Dimaya, 138 S. Ct. 

1204, 1228 (2018) (Gorsuch, J., concurring). Rather, those two branches “must respect 

the role of the Legislature, and take care not to undo what it has done.” King v. Burwell, 

135 S. Ct. 2480, 2496 (2015). In short, Congress must fix any flaw that may exist in a 
2 

particular piece of unambiguous legislation; the Executive and the Judiciary may not do 

so no matter how tempting the fix may be. 

Today we encounter an example of unambiguous legislation that neither the 

Executive nor the Judiciary may cast asunder: the National Firearms Act (NFA), 26 

U.S.C. §§ 5801–72. As the majority notes, that law regulates “machinegun[s],” which 

comprise “any weapon which shoots, is designed to shoot, or can be readily restored to 

shoot, automatically more than one shot, without manual reloading, by a single function 

of the trigger.” 26 U.S.C. § 5845(b). That clear language leaves little wiggle room. The 

word “automatically,” for instance, takes on its usual definition and refers to mechanisms 

that are “self-acting or self-regulating” rather than mechanisms that are not self-acting or 

self-regulating. And the phrase “single function of the trigger” speaks only about the 

trigger itself; the phrase mentions nothing about the external stimulus that interacts with 

the trigger. Thus, to qualify as a machine gun under the NFA, a firearm must satisfy at 

least two conditions: (1) the trigger itself must “function” only once to fire more than one 

shot, and (2) the mechanism that allows the trigger to “function” only once must be “selfacting or self-regulating.” 

As I explain below, a semiautomatic firearm equipped with a bump stock satisfies 

neither of those conditions. For one thing, the trigger on such a firearm must still 

“function” every time a shot is fired. And in any event, the bump stock—at least the 

nonmechanical variety—is not “self-acting or self-regulating” on the trigger. Why? 

Because the user of the firearm must also apply constant forward pressure with his or her 
3 

nontrigger hand for the bump stock to work.1

 So does a bump stock increase the speed 

by which the user can fire rounds? Yes. But does that mean the firearm to which it is 

attached is a machine gun under the NFA? No. 

Yet the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) now thinks 

so. In the wake of the tragic Las Vegas shooting, ATF promulgated a final administrative 

rule in late 2018 that classifies “bump-stock-type devices” as “machinegun[s]” under the 

NFA. See Bump-Stock-Type Devices, 83 Fed. Reg. 66,514 (Dec. 26, 2018) (the BumpStock Rule). ATF declared that a machine gun includes 

a device that allows a semiautomatic firearm to shoot more than one shot 

with a single pull of the trigger by harnessing the recoil energy of the 

semiautomatic firearm to which it is affixed so that the trigger resets and 

continues firing without additional physical manipulation of the trigger by 

the shooter. 

Id. at 66,553–54. 

That rule cannot withstand judicial scrutiny. As applied, the Bump-Stock Rule 

focuses on the user’s trigger finger instead of the trigger itself, which flouts the phrase 

“single function of the trigger” in the NFA. 26 U.S.C. § 5845(b) (emphasis added). The 

Bump-Stock Rule also fails to consider that the user must apply constant forward 

pressure with his or her nontrigger hand (a task that requires a fair amount of strength and 

dexterity) to make the bump stock work, which runs afoul of the word “automatically” in 

the NFA. Our inquiry should begin and end with that straightforward statutory analysis. 

1

 Mechanical bump stocks use slightly different mechanisms. The Akins 

Accelerator, for instance, uses internal springs instead of constant forward pressure to 

propel the firearm forward. 
4 

I therefore must respectfully dissent from the majority’s conclusion that the NFA’s 

definition of a machine gun is ambiguous as applied to bump stocks and that we must 

uphold the Bump-Stock Rule through Chevron deference. Neither the Judiciary nor the 

Executive has the power to make or change law by creating an ambiguity where none 

exists. To do so (as both ATF did and the majority does today) subverts the 

constitutional prerogatives of each branch of government. 

To be clear: I express no opinion on whether the Second Amendment protects 

bump stocks, nor do I express an opinion about whether any American citizen even has a 

valid reason to own a bump stock. Neither of those inquiries is before us today, and I do 

not base my dissent on any personal convictions about how a court should answer them. 

Rather, I dissent simply because the unambiguous language of the NFA establishes that 

Plaintiff W. Clark Aposhian is likely to succeed on the merits of his challenge to the 

Bump-Stock Rule. And in any event, even if the NFA’s language were ambiguous, I 

cannot endorse the majority’s decision to uphold the Bump-Stock Rule through Chevron 

deference. Applying Chevron is misguided for two distinct reasons: ATF disavowed that 

doctrine in its briefing, and the definition of “machinegun” in the NFA carries criminal 

consequences. Finally, ATF waived its argument that Plaintiff will not suffer any 

irreparable harm, which simply bolsters the conclusion that Plaintiff is entitled to 

preliminary injunctive relief.2

2

 The majority relies on the reasoning in the D.C. Circuit’s opinion in Guedes v. 

Bureau of Alcohol, Tobacco, Firearms & Explosives, 920 F.3d 1 (D.C. Cir. 2019), cert. 

denied, 140 S. Ct. 789 (2020). I agree with Judge Henderson’s thoughtful and wellcrafted partial dissent in that case. 
5 

I. 

 Consider again how a nonmechanical bump stock operates. The bump stock 

replaces the standard stock of a rifle—the part of the gun that rests against a shooter’s 

shoulder. A shooter pulls the trigger. The kickback or recoil causes the gun to slide 

backward. The shooter keeps his or her trigger finger stationary, maintaining backward 

pressure on the trigger. At the same time, the shooter must also apply forward pressure 

with his or her non-shooting hand. This process of forward pressure with one hand and 

backward pressure with the other causes the firearm to slide back and forth rapidly, 

which bumps the stationary finger against the moving trigger. The result: the trigger 

resets rapidly, which causes the rifle to fire many shots over a short time. Bump-Stock 

Type Devices, 83 Fed. Reg. at 66,516. 

ATF believes that process transforms a firearm into a weapon that shoots more 

than one shot “automatically . . . by a single function of the trigger.” 26 U.S.C. 

§ 5845(b). To get there, ATF first clarified in the Bump-Stock Rule that the word 

“automatically” means “functioning as the result of a self-acting or self-regulating 

mechanism that allows the firing of multiple rounds through a single function of the 

trigger.” Bump-Stock-Type Devices, 83 Fed. Reg. at 66,553; see also 27 C.F.R. 

§ 447.11. It next clarified that the phrase “single function of the trigger” means “single 

pull of the trigger and analogous motions.” Bump-Stock-Type Devices, 83 Fed. Reg. at 

66,553; see also 27 C.F.R. § 447.11. And it finally concluded that those clarifying 

definitions cover bump stocks: 
6 

[W]hen a shooter who has affixed a bump-stock-type device to a 

semiautomatic firearm pulls the trigger, that movement initiates a firing 

sequence that produces more than one shot. And that firing sequence is 

“automatic” because the device harnesses the firearm’s recoil energy in a 

continuous back-and-forth cycle that allows the shooter to attain continuous 

firing after a single pull of the trigger, so long as the trigger finger remains 

stationary on the device’s ledge (as designed). 

Bump-Stock-Type Devices, 83 Fed. Reg. at 66,519 (emphases added). 

 I take no issue with ATF’s definitions that clarify the meanings of “automatically” 

and “single function of the trigger.” But as I explain below, applying those definitions to 

nonmechanical bump stocks cannot lead to ATF’s preferred result. I discuss each in turn. 

A. 

I begin with the phrase “single function of the trigger.” As mentioned, the BumpStock Rule defines that phrase to mean “a single pull of the trigger and analogous 

motions.” 27 C.F.R. § 447.11. When one dissects that language, the reason it cannot 

apply to bump stocks becomes apparent. 

To start, I agree with the majority that the word “function” means “action.” 

Webster’s New International Dictionary 876 (1933). That much is clear. But I part ways 

with the majority when it concludes that the “statute is silent” (and therefore ambiguous) 

as to whether that action centers on “the movement of the trigger, or the movement of the 

trigger finger.” 

In fact, the statute speaks clearly: the function/action must be “of the trigger.” The 

NFA mentions nothing about trigger finger or any other “external impetus” that happens 

to interact with the trigger. Guedes v. Bur. of Alcohol, Tobacco, Firearms & Explosives, 

920 F.3d 1, 43 (D.C. Cir. 2019) (Henderson, J., concurring in part and dissenting in part) 
7 

(observing that the word “function” in the NFA “focus[es] on how the trigger acts”). 

And given that omission, we must presume “that [the] legislature says . . . what it means 

and means . . . what it says”—that is, we must presume that the function/action of the 

trigger itself is the only variable that matters. Henson v. Santander Consumer USA Inc., 

137 S. Ct. 1718, 1725 (2017) (alterations in original) (quoting Dodd v. United States, 545 

U.S. 353, 357 (2005)). By concluding otherwise and allowing an inquiry into the trigger 

finger, the majority effectively “replac[es] the actual text” of the NFA “with speculation 

as to Congress’ intent.” Magwood v. Patterson, 561 U.S. 320, 334 (2010). That the 

majority cannot do without taking on a legislative role. As a result, Congress’s use of the 

phrase “single function of the trigger” in the NFA can mean only “single action of the 

trigger” and not “single action of the trigger finger.” The clear language ties our hands. 

Necessarily, then, ATF’s interpretation of the phrase “single function of the 

trigger”—i.e., “single pull of the trigger and analogous motions”—can refer only to the 

action of the trigger and not the trigger finger. See Guedes, 920 F.3d at 43 (D.C. Cir. 

2019) (Henderson, J., concurring in part and dissenting in part) (“[N]othing in the 

[Bump-Stock] Rule’s definition refers to a shooter’s finger or a volitional action.”). That 

is the only way for ATF’s interpretation to remain valid. Otherwise, ATF’s interpretation 

would contradict the unambiguous NFA—the interpretation would refer to the trigger 

finger, while the statute refers to the trigger alone—and “[a] regulation in conflict with 
8 

the terms of an unambiguous statute will not be sustained.” Burnet v. Marston, 57 F.2d 

611, 612 (D.C. Cir. 1932).3 

That limitation on the phrase “single pull of the trigger and analogous motions” 

sounds the death knell for ATF’s new take on bump stocks. For as I alluded to above, a 

semiautomatic rifle equipped with a bump stock simply does not use a single function of 

the trigger to fire more than one shot. 

 To illustrate, first consider the basic mechanics of a semiautomatic rifle that lacks 

a bump stock. The trigger on that type of rifle must necessarily “pull” backwards and 

release the rifle’s hammer—the part of a rifle that sets in motion how the bullet leaves the 

barrel—every time that the rifle discharges. See Plaintiff-Appellant’s App’x A73–A74. 

The rifle cannot fire a second round until both the trigger and hammer reset. Only then 

can the trigger “pull” backwards once more and reinitiate the entire firing process from 

the beginning. 

A bump stock cannot change that process. The trigger on a semiautomatic rifle 

equipped with a bump stock still pulls backwards every time that the rifle fires. The only 

difference is that recoil—not the operator’s finger—causes that pull. See Guedes, 920 

3

 The majority points out that the parties agree that ATF’s interpretation refers to 

the action of the shooter’s trigger finger. But that agreement does not help the majority 

in any way. Again, if the regulation does refer to the motion of the trigger finger, the 

regulation is invalid because it conflicts with the unambiguous NFA. Burnet, 57 F.2d at 

612 (“While the [agency] was clothed with authority to promulgate regulations, [it] was 

not authorized to add to or take from the plain language of the statute, for, ‘where the 

intent is plain, nothing is left to construction.’” (quoting United States v. Fisher, 6 U.S. (2 

Cranch) 358, 386 (1805)). I simply choose to give the regulation the benefit of the doubt. 
9 

F.3d at 48 (Henderson, J., concurring in part and dissenting in part) (“A semiautomatic 

rifle shoots a single round per pull of the trigger and the bump stock changes only how

the pull is accomplished.” (emphasis in original)). Again, the NFA demands that we look 

only to how the trigger acts. And given that the trigger functions every time a 

semiautomatic rifle equipped with a bump stock fires a round, such a rifle unambiguously 

cannot be a machine gun under the NFA even if the operator’s trigger finger remains 

stationary. 

Contrasting a bump-stock-equipped rifle with the machine gun that the majority 

references from our decision in United States v. Oakes, 564 F.2d 384 (10th Cir. 1977), 

reinforces my point. The gun in Oakes contained two “projections” in the area that a 

traditional trigger usually occupies. Id. at 388. The first was a “forward” projection 

“curved so as to fit the finger in a normal fashion”—in other words, it looked like and 

functioned as a regular trigger. Id. The second projection was “seated behind” the 

forward one and “curved in a manner so that at its extremity it would be pushed if the 

[shooter fully pulled the forward projection] to contact.” Id. In sum, when the shooter 

fully pulled the first projection/trigger, the second projection activated and “fully 

automated the gun.” Id. 

The question in Oakes was whether that interplay between the two projections 

allowed the gun to fire more than one shot “by a single function of the trigger”; the 

government argued it did, while the gun owner argued that the gun’s “two triggers” 

meant it did not. Id. at 387 n.2, 388. Contra the majority’s suggestion today, the ultimate 

answer to that question did not hinge on the shooter’s volitional actions in any way. 
10 

Indeed, the holding of Oakes that the weapon fit the bill of a machine gun under the NFA 

boiled down to the fact that “fully pulling the trigger”—that is, the forward projection—

allowed the gun to automatically fire rounds. Id. at 388. That rationale endures even if 

one focuses on the shooter’s trigger finger or the trigger itself: both the finger and the 

trigger on such a gun “pulled” just once to fire more than one round even though a 

second, posterior projection factored into the weapon’s automatic mechanism. See id. 

We should thus draw little guidance from the language in Oakes that speaks in terms of 

the shooter’s actions rather than the trigger’s actions. The distinction between the two 

concepts made no difference to the holding, so that specific language in Oakes is no more 

than imprecise dicta. Tokoph v. United States, 774 F.3d 1300, 1303 (10th Cir. 2014) 

(“[A] panel of this court is bound by a holding of a prior panel of this court but is not 

bound by a prior panel’s dicta.” (alteration and emphasis in original) (quoting Bates v. 

Dep’t of Corr., 81 F.3d 1008, 1011 (10th Cir. 1996))). 

Viewed under that lens, Oakes supports my position. That case tracks the text of 

the NFA: it does not defy the congressional determination that the trigger itself must 

function just once to fire more than one shot. As I explain above, however, a rifle 

equipped with a bump stock does not fit that rubric. That type of rifle continues to use 

multiple functions of the trigger itself even though the shooter must take only a single 

volitional action. A bump stock, in other words, changes only how a trigger pulls; it does 

not change the fact that the trigger itself must function every shot. Under the 

unambiguous language of the NFA, that means that a bump stock cannot transform a 

semiautomatic rifle into a machine gun. 
11 

B. 

The word “automatically” in the NFA unearths an even-more-obvious flaw in the 

ATF’s bump-stock ban. 

As a reminder, I take no issue with the ATF’s interpretation of that word—i.e., 

“functioning as the result of a self-acting or self-regulating mechanism that allows the 

firing of multiple rounds through a single function of the trigger.” 27 C.F.R. § 447.11. 

That interpretation “reflects the ordinary meaning of that term at the time of the NFA’s 

enactment in 1934,” and that same ordinary meaning continues to this day. Bump-StockType Devices, 83 Fed Reg. at 66,519; see also Webster’s New International Dictionary 

187 (2d ed. 1934) (defining “automatic” as “[h]aving a self-acting or self-regulating 

mechanism that performs a required act at a predetermined point in an operation”); 

Automatic, Merriam-Webster.com Dictionary, https://www.merriamwebster.com/dictionary/automatic (last visited Mar. 30, 2020) (defining “automatic” as 

“having a self-acting or self-regulating mechanism”). 

The problem is again one of application. A nonmechanical bump stock is not a 

“self-acting or self-regulating mechanism”; the constant forward pressure that the shooter 

must apply with his or her nontrigger hand prevents that label.4 

4

 In her dissent, Judge Henderson does question the ATF’s actual interpretation of 

the word “automatically.” See Guedes, 920 F.3d at 42 (Henderson, J., concurring in part 

and dissenting in part) (“Although the [Bump-Stock] Rule . . . correctly interprets ‘single 

function of the trigger,’ it misreads ‘automatically.’”). But her reasons for that belief also 

stem from the constant forward pressure that the shooter must apply with his or her 

nontrigger hand. Id. at 43–45. Thus, no matter if the interpretation or application of the 

word “automatically” is the ultimate problem, the important point is that the “extra” 
12 

In coming to this conclusion, I do no more and no less than take the words “selfacting” and “self-regulating” at face value. If a mechanism is self-acting, it acts by itself. 

If it is self-regulating, it regulates itself. A nonmechanical bump stock does neither. By 

design, that type of bump stock requires manual human input—constant forward pressure 

with the nontrigger hand—to act. And it requires that same manual human input to 

regulate its actions. Without the constant forward pressure, a nonmechanical bump stock 

simply will not work; the firearm to which it is attached will fire only one shot even with 

the stationary trigger finger applying constant backward pressure. A nonmechanical 

bump stock is therefore not “self-acting” or “self-regulating.” 

That straightforward logic also highlights the flaws underlying the majority’s 

attempt at fashioning an ambiguity from the word “automatically.” Again, the terms 

“self-acting” and “self-regulating” are self-explanatory—they exclude any manual human 

involvement by their very definitions. So the majority is simply wrong when it says that 

the NFA is ambiguous by failing to delineate the precise amount of necessary human 

input. The ordinary, dictionary definition of “automatically” makes the answer clear: 

none. 

The D.C. Circuit tried to make the majority’s exact point by example. It observed, 

for instance, that even automatic weapons “require both a single pull of the trigger and

the application of constant and continuing pressure on the trigger after it is pulled.” 

Guedes, 920 F.3d at 30 (majority opinion) (emphasis in original). It also analogized an 

physical input from the nontrigger hand prevents us from classifying nonmechanical 

bump-stock-type devices as machine guns.
13 

automatic firearm to an automatic sewing machine that “requires the user to press a pedal 

and direct the fabric.” Id. (emphasis in original). Because these automatic devices 

require some human interaction, the D.C. Circuit posited that the word “automatically” 

remains ambiguous as to the precise amount of human input that word permits. 

But examples such as these only prove my ultimate point. Unlike a 

nonmechanical bump stock, the human involvement in a fully automatic firearm and an 

automatic sewing machine is not a part of their mechanisms themselves. Instead, the 

involvement is in some way extrinsic to their actual mechanisms. And that makes all the 

difference, because the terms “self-acting” and “self-regulating” only modify the word 

“mechanism.” See 27 C.F.R. § 447.11 (“[T]he term ‘automatically’ . . . means 

functioning as the result of a self-acting or self-regulating mechanism . . . .” (emphasis 

added)). The continued pressure on the trigger of an automatic firearm, for example, is 

not part of the internal mechanism that keeps feeding cartridges into and ejecting 

cartridges out of the firearm’s chamber at a rapid pace. The constant pedal-pressure on 

an automatic sewing machine is the same way: although that pressure keeps the 

automatic process going, the pressure is not itself part of the engineered mechanism that 

forces the needle to bob up and down. Directing the fabric through an automatic sewing 

machine is an even clearer example, because even if the sewer stops feeding fabric, the 

automatic mechanism can continue to operate. 

By contrast, nonmechanical bump stocks require manual human involvement at all 

times as part of their underlying mechanisms. As I’ve previously explained, these types 

of bump stocks increase a user’s firing rate through recoil. And recoil is impossible 
14 

without constant forward pressure from the user’s nontrigger hand. The former hinges on 

the latter: no manual human input, no recoil. In other words, manual human input is a 

necessary element of a nonmechanical bump stock’s actual mechanism, which separates 

this type of bump stock from the examples that the D.C. Circuit put forth. 

For all of these reasons, a nonmechanical bump stock is not a “self-acting or selfregulating mechanism.” And because it is not self-acting or self-regulating, the firearm 

to which it is attached is unambiguously not one that shoots “automatically.” 

C. 

 In sum, both the word “automatically” and the phrase “single function of the 

trigger” in the NFA are unambiguous as applied to nonmechanical bump stocks. Plaintiff 

is thus likely to succeed on the merits of his challenge to the Bump-Stock Rule. 

II. 

Because the NFA’s terms are unambiguous, the majority inappropriately applied 

Chevron deference to the Bump-Stock Rule. But even if that statute were ambiguous, at 

least two other reasons counsel against applying Chevron. 

First, the government explicitly disavowed any reliance on Chevron. That alone 

should have prevented the majority from applying the controversial doctrine. As Justice 

Gorsuch recently observed in another case about the Bump-Stock Rule, “[i]f the 

justification for Chevron is that ‘policy choices’ should be left to executive branch 

officials ‘directly accountable to the people,’ then courts must equally respect the 

Executive’s decision not to make policy choices in the interpretation of Congress’s 

handiwork.” Guedes v. Bureau of Alcohol, Tobacco, Firearms & Explosives, 140 S. Ct. 
15 

789, 790 (2020) (statement of Gorsuch, J., respecting denial of certiorari) (emphasis in 

original) (quoting Epic Sys. Corp., 138 S. Ct. at 1630). By doing the exact opposite—

that is, turning a blind eye to the government’s request and applying Chevron anyway—

the majority “place[s] an uninvited thumb on the scale in favor of the government.” Id. 

(statement of Gorsuch, J., respecting denial of certiorari). That concerns me, especially 

given that both the Supreme Court and our Circuit have “often declined to apply Chevron 

deference when the government fails to invoke it” or otherwise rely on it. Id. (statement 

of Gorsuch, J., respecting denial of certiorari); see also, e.g., Hays Med. Ctr. v. Azar, — 

F.3d —, No. 17-3232, 2020 WL 1922595, at *13 n.18 (10th Cir. Apr. 21, 2020); Hydro 

Res., Inc. v. EPA, 608 F.3d 1131, 1146 (10th Cir. 2010). If any of our precedent holds 

otherwise, see, e.g., TransAm Trucking, Inc. v. Admin. Review Bd., 833 F.3d 1206, 1212 

n.4 (10th Cir. 2016), perhaps the day will soon come when the Supreme Court 

definitively overrules it.

Second, because the definition of “machinegun” in the NFA “carries the 

possibility of criminal sanctions,” Chevron is likewise inapplicable. Guedes, 140 S. Ct. 

at 790 (statement of Gorsuch, J., respecting denial of certiorari); see also 18 U.S.C. 

§ 922(o)(1) (“[I]t shall be unlawful for any person to transfer or possess a machinegun.”); 

18 U.S.C. § 921(a)(23) (“The term ‘machinegun’ has the meaning given such term in 

section 5845(b) of the National Firearms Act.”). I need not belabor the point; many other 

jurists have written about this concern in great detail. See, e.g., Guedes, 140 S. Ct. at 790 

(statement of Gorsuch, J., respecting denial of certiorari); Guedes, 920 F.3d at 39–42 

(Henderson, J., concurring in part and dissenting in part); Gutierrez-Brizuela v. Lynch, 
16 

834 F.3d 1142, 1155–57 (10th Cir. 2016) (Gorsuch, J., concurring); Esquivel-Quintana v. 

Lynch, 810 F.3d 1019, 1027–32 (6th Cir. 2016) (Sutton, J., concurring in part and 

dissenting in part), rev’d on other grounds sub nom. Esquivel-Quintana v. Sessions, 137 

S. Ct. 1562 (2017). Suffice to say that when, as here, a law carries both civil and 

criminal consequences, applying Chevron can lead to troubling and unintended outcomes. 

After all, “[b]ecause a single law should have a single meaning, the ‘lowest common 

denominator’—including all rules applicable to the interpretation of criminal laws—

governs all of its applications.” Esquivel-Quintana, 810 F.3d at 1028 (Sutton, J., 

concurring in part and dissenting in part) (quoting Clark v. Martinez, 543 U.S. 371, 380 

(2005)). That approach is the only way to ensure that the law takes on “the least libertyinfringing interpretation.” Id. Thus, since “[t]he Supreme Court has expressly instructed 

us not to apply Chevron deference when an agency seeks to interpret a criminal statute,” 

Gutierrez-Brizuela, 834 F.3d at 1155 (Gorsuch, J., concurring) (emphasis in original), the 

logical result is that we must also not apply Chevron when a statute has both civil and 

criminal applications. 

With that said, the majority correctly observes that, more than once, we have given 

at least some deference to an agency’s interpretation of a statute carrying criminal 

repercussions. See, e.g., United States v. Hubenka, 438 F.3d 1026, 1032–34 (10th Cir. 

2006); United States v. Atandi, 376 F.3d 1186, 1189 (10th Cir. 2004); NLRB v. Okla. 

Fixture Co., 332 F.3d 1284, 1287 (10th Cir. 2003) (en banc). And despite the Supreme 

Court’s recent guidance condemning Chevron in the criminal sphere, some courts (like the 

majority today) believe that the Supreme Court’s language in an earlier case muddies the 
17 

waters. Compare Abramski v. United States, 573 U.S. 169, 191 (2014) (“[C]riminal laws 

are for courts, not for the Government, to construe.”), and United States v. Apel, 571 U.S. 

359, 369 (2014) (“[W]e have never held that the Government’s reading of a criminal statute 

is entitled to any deference.”), with Babbitt v. Sweet Home Chapter of Cmties. for a Great 

Or., 515 U.S. 687, 703–04 & n.18 (1995) (“[W]e owe some degree of deference to [the 

agency’s] reasonable interpretation” of a “statute [that] includes criminal penalties.”). See 

also Guedes, 920 F.3d at 25 (majority opinion) (drawing fine lines between Abramski, 

Apel, and Babbitt to give Chevron a foothold when a statute carrying criminal 

repercussions is at play). 

Against this backdrop, my hope is that the Supreme Court will one day take up this 

issue to give us clear guidance for future cases. Whatever the benefits of Chevron are, 

none come to mind by forcing courts to expand the doctrine to statutes that bring about 

dual civil and criminal consequences. 

III. 

As a final point, I disagree with the majority’s conclusion that Plaintiff has not met 

his burden of proving that he would suffer irreparable harm absent an injunction. My 

reason is simple: the government conceded outright in the district court that Plaintiff 

would suffer irreparable harm by complying with the regulation. When a party 

intentionally relinquishes or abandons a theory in the district court, “we usually deem it 

waived and refuse to consider it” on appeal. Richison v. Ernest Group, Inc., 634 F.3d 

1123, 1127 (10th Cir. 2011). We should follow that rule; hold the government to its 
18 

intentional waiver; and conclude that Plaintiff, given that waiver, has met his burden of 

establishing irreparable harm. 

The majority retorts that our decision in Dominion Video Satellite, Inc. v. 

EchoStar Satellite Corp., 356 F.3d 1256 (10th Cir. 2004), forbids that conclusion. The 

majority is mistaken. True enough, we held in Dominion that a party moving for a 

preliminary injunction could not establish irreparable harm simply by invoking a 

contractual stipulation to that fact. Id. at 1261, 1266. Even so, the opposing party in 

Dominion had argued in the district court that the question of irreparable harm should not 

hinge on the contractual stipulation alone. See, e.g., id. at 1261 (observing that the 

district court, “[i]n making its irreparable harm determination,” rejected some of the 

moving party’s arguments “[b]ased on evidence presented by” the opposing party); id. 

(noting the district court’s belief that the opposing party’s expert witnesses “persuasively 

demonstrated” the moving party would suffer a quantifiable loss). And therein lies the 

pivotal difference between Dominion in our case today: the opposing party in Dominion 

never intentionally waived its position on irreparable harm in court, while the opposing 

party in our case (ATF) did waive its position in court. A prelitigation stipulation that a 

party later challenges once the conflict comes to a head is far different than conceding an 

element of a claim to a judge. In short, the majority compares apples and oranges. 

At bottom, the majority’s position means that a party with the burden of proof 

cannot overcome its burden by pointing out that the opposing party conceded an element 

of the claim in court. As one would expect, that alarming consequence skirts circuit 

precedent. See, e.g., Johnson v. Spencer, 950 F.3d 680, 708 (10th Cir. 2020) (concluding 
19 

that defendants who had relied on claim preclusion as a defense met their burden of proof 

on two of the three requisite elements because the opposing party “concede[d] . . . the 

second and third elements”); United States v. Sinks, 473 F.3d 1315, 1321 (10th Cir. 

2007) (observing that the government can concede elements of the plain error standard of 

review, which a criminal defendant has the burden of proof to establish). And given that 

precedent (and, for that matter, common judicial practice), the fact that Plaintiff and ATF 

had different views in the district court about the type of irreparable harm at issue is 

irrelevant. Because ATF conceded point blank that Plaintiff would suffer some

irreparable harm—one of the four elements of any preliminary injunction—Plaintiff’s 

failure to correctly identify the exact parameters of that harm has no legal effect.5

The majority thus fails to posit a defensible reason for rewarding ATF’s aboutface on appeal. And I myself cannot think of any good reason to do so when strong 

counterarguments—for example, that bump stocks are unique pieces of property, that the 

Bump-Stock Rule can lead to criminal consequences, and so on—suggest that ATF 

would (or at least should) lose on the irreparable-harm element in any event. I would 

5

 The same logic applies to the majority’s argument that a court’s ability to award 

Plaintiff compensatory damages for his bump stock precludes his harm from being 

irreparable. Even if the majority is correct—and I am not convinced it is, especially 

given that ATF has argued in at least one other case that bump stock owners are ineligible 

for compensation, Lane v. United States, No. 3:19-CV-01492-X, 2020 WL 1513470, at 

*1 (N.D. Tex. Mar. 30, 2020)—that nuance makes no difference today. Again, because 

ATF conceded irreparable harm, Plaintiff’s purported ability to receive compensatory 

damages does not matter. 

 
20 

therefore hold ATF to its intentional waiver and conclude that Plaintiff will suffer 

irreparable harm from the Bump-Stock Rule.6

IV. 

For all these reasons, I would reverse the district court’s denial of a preliminary 

injunction. I respectfully dissent. 

6

 Absent waiver, I agree that Plaintiff cannot use our holding in Free the NippleFort Collins v. City of Fort Collins, 916 F.3d 792 (10th Cir. 2019), that “[a]ny 

deprivation of any constitutional right” amounts to irreparable harm. Id. at 806. Plaintiff 

makes no constitutional arguments today (he only makes statutory and administrative 

arguments), so the language from Free the Nipple goes nowhere from the start. With that 

said, in an appropriate case, we should consider revisiting (or at least limiting) that 

specific holding from Free the Nipple. Allowing any deprivation of any constitutional 

right to serve as per se irreparable harm is a far-too-powerful tool in most cases.